The pack is a good design, startlingly light, and can hold a fair bit of stuff. The strap design is welcome as well, with good support from the chest and waist straps when used, and the waist straps being very easily removed and replaced.
However, the weatherproofing is a joke. I didn't expect this pack to withstand a monsoon but I wouldn't even call it water resistant. The pack soaks through quickly and items in it get wet, whether bicycling in light rain or skiing in conditions well below freezing. I don't trust it to keep anything dry in any conditions, which is very disappointing.
If you're going to be in the dry I'd recommend it - it's very light, and comfortable.
If you're going to be seeing any rain, snow or heck heavy fog, I'd either buy something else or plan to use a dry-bag liner.